Alright so here is my take on a Dimir (U/B) mill/exile deck along with a sideboard. First off I'd like to say during my test runs against mono-blue devotion, G/W populate tokens and a U/W control, I won roughly 90% of my games because it is fairly fast and consistent. With that being said, I am looking for some input to make it more controlling and slightly faster, +1's and constructive criticism is always welcome with an explanation of why you believe it to be a better swap.
Card Explanations Mainboard:
Ashiok, Nightmare Weaver: All around powerhouse. exiles cards from library and steals creatures. -10 only used against control decks.
Jace, Memory Adept: Top 10 mill, need I say more?
Liliana of the Dark Realms: Lets me tutor for swamps thinning my deck out, also the emblem is good to have if she lives that long to overload the crap out of Mind Grind.
Far / Away: Creature control early to mid game, bounce and sacrifice.
Breaking / Entering: 2 mana for mill 8 cards? Yes please. Better than Tome Scour.
Mind Grind: Has the possibility of being devastating to Aggro decks who don't run more than 20-22 lands.
Consuming Aberration: Possibility of being huge, also his second ability of mill until opponent hits a land after successful cast is always nice.
Lazav, Dimir Mastermind: Self explanatory, he becomes a large creature I put into an opponents graveyard, survives kill spells and Detention Sphere.
Nightveil Specter: Has potential to be nasty if he goes unchecked. Also, great for devotion.
Hero's Downfall: Kills powerhouses, Elspeth, Sun's Champion and Jace, Architect of Thought in control decks.
Traumatize: All around a good milling utility.
Wight of Precinct Six: also has the potential to be a large body unless playing against control. If, then blocker he shall become.
Card Explanations Sideboard:
Jace, Memory Adept: Milling top 10 every turn for more consistent milling ability.
Dissolve: In case I need a few counter spells for some devastating heavy hitters.
Traumatize: 3rd in sideboard for an extra utility for some more mill ability.
Crypt Incursion: If I fall low in life, this has potential to save by butt.
Lazav, Dimir Mastermind: Just cuz.
Mind Grind: Extra one against Aggro-ish decks.
Consuming Aberration: Large Creature potential.
Pithing Needle: For them pesky planeswalkers and the one man army know as AEtherling!
Ratchet Bomb: Against token/populate decks, also helps against Elspeth, Sun's Champion's token production.
I would like some advice if Reap Intellect or Thassa, God of the Sea's Scry mechanic could be of some use.